The human ras proteins are members of a superfamily of low molecular weight GTP-binding proteins. While considerable experimental evidence provides strong support for a role of the ras proteins in malignant transformation, to date, no other member of the ras superfamily has been identified as oncogene proteins. However, recent observations have provided support that members of one branch of ras-related proteins, the rho subfamily (rac1 and 2, rho A,B,C, and G, CDC42Hs, TC10) may contribute to the aberrant growth properties of malignant cells. First, elevated expression of rho proteins has been associated with enhanced cellular proliferation and alterations in cellular morphology. Second, truncated versions of three rho family regulatory proteins (dbl, vav, ect-2) have been identified as potent oncogene proteins. These three proteins are like to function as activators (exchange factors) of rho protein function, and may trigger transformation via chronic activation of rho protein function. Finally, there is evidence that oncogenic ras proteins mediate some aspects of malignant transformation via activation of rho family proteins. Altogether, these observations have prompted our studies to determine if aberrant function of rho family proteins, and of their regulatory proteins, contribute to malignant transformation. The specific aims of this proposal are (1) to assess the possibility that rho family proteins (racs and rhos) are potential oncogenes, (2) to determine if the full malignant phenotype triggered by oncogenic ras is dependent on rac and rho protein function, and (3) to determine if dbl family oncogenes trigger uncontrolled growth via deregulating rho protein function. The long-range goals of these studies will be to determine if aberrant rho function contributes to the malignant phenotype of human tumor cells and to determine how rho family proteins mediate changes in the actin cytoskeleton, focal adhesion plaques, and extracellular matrix that regulate cell-substratum interactions and cell motility.